[llvm] [RISCV] Shrink vslidedown when lowering fixed extract_subvector (PR #65598)

[Luke Lau via llvm-commits]

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@@ -8684,6 +8684,39 @@ SDValue RISCVTargetLowering::lowerEXTRACT_SUBVECTOR(SDValue Op,
       ContainerVT = getContainerForFixedLengthVector(VecVT);
       Vec = convertToScalableVector(ContainerVT, Vec, DAG, Subtarget);
     }
+
+    // The minimum number of elements for a scalable vector type, e.g. nxv1i32
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lukel97 wrote:

Didn't realise that extract_vector_elt was doing the same thing, thanks

https://github.com/llvm/llvm-project/pull/65598